This invention relates to a three-function pressure switch device adapted to be provided in the coolant passage on the higher pressure side of the cooling cycle circuit for the cooling device in an automobile and comprising a switch for interrupting the operation of a compressor by opening the electrical contacts on the cooling cycle circuit when the pressure on the higher pressure side of the cooling circuit abnormally decreases or increases and a switch capable of optionally determining pressure for opening or closing the electrical contacts.
There have been proposed and practically employed a variety of three-function pressure switches and the prior art three-function switches have been developed taking the backgrounds into consideration:
A. When the coolant in the cooling cycle circuit leaks out of the circuit to cause coolant shortage in the circuit, the compressor associated with the circuit tends to break. Especially, when the coolant shortage is substantial, the pressure on the higher pressure side decreases to an abnormal level and thus, it is necessary to provide a low pressure switch which senses the decrease in pressure and opens the electrical contacts of the circuit to thereby interrupt the operation of the compressor for prevention of breakage of the compressor.
B. When the cooling load on the cooling cycle circuit is excessively high or the capacity of the compressor decreases due to any cause, the pressure on the higher pressure side of the cooling cycle circuit increases to an abnormally high level. In such a case, it is required to interrupt the operation of the cooling cycle circuit and thus, for the purpose, there is the necessity for provision of a switch which senses such abnormally high pressure and opens the electrical contacts. However, when the operation of the compressor is interrupted in response to the abnormal increase in pressure, the pressure decreases rapidly to the normal level and the pressure switch returns to the normal condition in which the compressor resumes its operation. In such a case, if there is no differential pressure for opening and closing the switch, the switch frequently opens and closes and thus, the electrical contacts on the higher pressure side of the cooling cycle circuit should be provided with differential pressure.
C. In order to maintain the pressure on the higher pressure side of the cooling cycle circuit within a predetermined normal range regardless of the magnitude of cooling load when the pressure on the higher pressure side of the cooling cycle circuit at the normal level, in some cases, the compression capacity of the compressor is controlled. For this purpose, it is necessary to a mechanism which closes the electrical contacts so as to increase the compression capacity of the compressor when the pressure on the higher pressure side of the cooling cycle circuit exceeds a predetermined level and opens the electrical contacts when the pressure on the higher pressure side of the cooling cycle circuit drops to a value smaller than the predetermined value and it is also necessary to provide a pressure switch which responds to differential pressure for opening and closing the electrical contacts, respectively.
Any one of the above-mentioned three types of pressure switches have to be provided in the coolant passage on the higher pressure side of the cooling cycle circuit.
One example of the prior art three-function or complex pressre switches is shown in Japanese Laid-Open Utility Model Application No. 169,636/1983. The prior art three-function or complex pressure switch generally comprises a casing including an upper casing portion 2 provided with a center coaxial pressure inlet 1 and a lower casing portion 3 integrally connected to the upper casing portion, a diaphragm 4 pinched at the periphery between the upper and lower casing portions 2, 3 to define a pressure receiving chamber 6 in the upper casing portion 2, a piston assembly positioned within the upper casing portion below the diaphragm and including coaxial outer and inner pistons 13, 14 operable independently of each other, a spring-loaded vertically movable member 21 positioned within the lower casing portion 3 below the piston assembly for vertical movement in response to the vertical movement of the piston assembly and including a reduced diameter projection 29 extending downwardly therefrom, a first electrical switching section 45 mounted on a lower part of the lower casing portion 3 for opening and closing in accordance with an amount of the downward movement of the movable member 21, a spring 22 surrounding the movable member 21 for normally biasing the member upwardly against pressure acting on the upper surface of the piston assembly 13, 18 through the diaphragm 4, a resilient disc 35 extending across an upper portion of the movable member 21 in contact with the undersurface of the inner piston 18, and a second electrical switching section 37 mounted on the lower part of the lower piston portion 3 for opening and closing as the resilient disc resiliently warps in opposite directions.
Although the three-function pressure switch of the Japanese utility model application has the first electrical switching section 45 on the intermediate pressure side and the second electrical switching section 37 on the highest pressure side and the second electrical switching section 37 is associated with the resilient disc 35, the first electrical switching section 45 cannot be provided with any resilient disc because of the specific construction of the section. Thus, the pressure switch is manipulated by causing the electrical elements associated with the second electrical switching section 45 to engage with or disengage from each other by means of the movable member 21 to which external force is applied. However, a movable electrical wire has to be provided between the terminal electrically connected to the movable member and the external lead for operating the electrical elements which complicates the construction of the pressure switch and makes it difficult to assemble the switch.